Chelsea defender Gary Cahill believes Manchester United hitman Romelu Lukaku has become a world class striker since he left the Blues four years ago.
The Belgian striker moved to Stamford Bridge from Anderlecht in 2011 but struggled to make an impact, despite impressing in loan spells with West Brom and Everton.
Lukaku eventually moved to the Toffees on a permanent basis in 2014 where he scored 53 goals in 110 appearances, drawing praise from pundits and players alike.
After much speculation, the 25-year old was then signed by United for £90million last summer and, ahead of Saturday's FA Cup final, Cahill admitted he's been impressed with his former team-mate's progression.
"It'll be difficult. I've played against him and trained against him loads of times," Cahill said.
"The cup final's going to be whoever performs on the day. We've put the season to bed and we have a full week to prepare.
"When he was here he had talent but he was very young. He's developed into a world class striker so credit to him.
"Sometimes when you're at a club like Chelsea you feel sorry when you see a player move on, because naturally some progress and some don't. You don't hear about the ones that don't.
"We all know it's hard to have time to come in as a young player - maybe the club and the supporters give you seven, eight, nine games where you're rusty and not performing. It's difficult to do that.
"They've gone on and developed elsewhere, and he's gone on to be a top player. There's loads of them. What everyone can see - pace, power, strength and he can finish. His goalscoring record is very good."
Meanwhile, Chelsea have accepted a Football Association charge and been fined £20,000 after players and coaches surrounded referee Lee Mason at half-time during last Wednesday's 1-1 Premier League draw with Huddersfield.
The Blues were angered when Mason awarded the hosts a corner but then blew for half-time before it was taken by Willian.